Photocatalytic ozonation of monuron over suspended and immobilized TiO2–study of transformation, mineralization and economic feasibility

A comprehensive systematic review of photocatalytic degradation of pesticides using nano TiO2

This study has systematically reviewed all of the research articles about the photocatalytic degradation of pesticides using titanium dioxide (TiO₂) nanoparticles (NPs) and ultraviolet (UV) irradiation. Online databases were searched for peer-reviewed research articles and conference proceedings published during 2009-2019, and ultimately 112 eligible articles were included in the review. Fifty-three active ingredients of pesticides and one mixture had been investigated, most of them were organophosphorus (22%), followed by triazine derivatives (11%), chloropyridines (9%), and organochlorines (9%). Sixteen types of TiO₂ with an average photodegradation efficiency of 71% were determined. Based on the type of pesticide and experimental conditions such as irradiation time, the complete photodegradation had been observed. The removal of each group of pesticides has been sufficiently discussed in the article. Effect of experimental conditions on photocatalytic activity has been investigated using linear and polynomial regressions. The strategies to reduce the required energy for this process, doping TiO₂ with metal and non-metal agents, innovative reactor designs, etc., were also discussed. In conclusion, TiO₂ NPs have been successful for degradation of pesticides. Future direction for research incorporates developing and application of heterogeneous doped and immobilized titania having optimized characteristics such as surface area, reactive centers, recombination rate, and phase, and capable to photo-degrade low levels of pesticides residues under solar light in an efficient full-scale size.

Innovative and Cost-Efficient BiOI Immobilization Technique on Ceramic Paper-Total Coverage and High Photocatalytic Activity

In the present work, visible light active bismuth oxyiodide (BiOI) was immobilized on a commercial, non-conductive support (an Al2O3 based ceramic paper) using a novel two-step spray coating technique and investigated with different characterization methods (e.g., SEM, Raman, XPS). Our main goal was to eliminate the separation costs after the photocatalytic measurement and investigate the chemical relevance and opportunity to use this technique in the industry. Our as-prepared uniform BiOI layer had similar properties to the well-known reference BiOI powder. The Raman and XPS measurements confirmed that the enriched amount of the surface iodine defined the color and as well the band gap of the BiOI layer. The durable BiOI layers have prominent photocatalytic activity under UV and visible light irradiation as well. The scale-up procedure proved that the designed BiOI coated paper was reusable and potentially applicable in the industry by straightforward scale-up, which is due to the elaborated non-conventional BiOI coverage estimation method. This immobilization technique could open several opportunities for immobilizing many other visible light active photocatalysts with simple materials and low cost.

Utilization of Carbon Nanospheres in Photocatalyst Production: From Composites to Highly Active Hollow Structures

Titanium dioxide–carbon sphere (TiO₂–CS) composites were constructed via using prefabricated carbon spheres as templates. By the removal of template from the TiO₂–CS, TiO₂ hollow structures (HS) were synthesized. The CS templates were prepared by the hydrothermal treatment of ordinary table sugar (sucrose). TiO₂–HSs were obtained by removing CSs with calcination. Our own sensitized TiO₂ was used for coating the CSs. The structure of the CSs, TiO₂–CS composites, and TiO₂–HSs were characterized by scanning electron microscopy (SEM), infrared spectroscopy (IR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and diffuse reflectance spectroscopy (DRS). The effect of various synthesis parameters (purification method of CSs, precursor quantity, and applied furnace) on the morphology was investigated. The photocatalytic activity was investigated by phenol model pollutant degradation under visible light irradiation (λ > 400 nm). It was established that the composite samples possess lower crystallinity and photocatalytic activity compared to TiO₂ hollow structures. Based on XPS measurements, the carbon content on the surface of the TiO₂–HS exerts an adverse effect on the photocatalytic performance. The synthesis parameters were optimized and the TiO₂–HS specimen having the best absolute and surface normalized photocatalytic efficiency was identified. The superior properties were explained in terms of its unique morphology and surface properties. The stability of this TiO₂–HS was investigated via XRD and SEM measurements after three consecutive phenol degradation tests, and it was found to be highly stable as it entirely retained its crystal phase composition, morphology and photocatalytic activity.

Facile Green Synthesis of BiOBr Nanostructures with Superior Visible-Light-Driven Photocatalytic Activity

Novel green bismuth oxybromide (BiOBr-G) nanoflowers were successfully synthesized via facile hydrolysis route using an Azadirachta indica (Neem plant) leaf extract and concurrently, without the leaf extract (BiOBr-C). The Azadirachta indica leaf extract was employed as a sensitizer and stabilizer for BiOBr-G, which significantly expanded the optical window and boosted the formation of photogenerated charge carriers and transfer over the BiOBr-G surface. The photocatalytic performance of both samples was investigated for the degradation of methyl orange (MO) and phenol (Ph) under the irradiation of visible light. The leaf extract mediated BiOBr-G photocatalyst displayed significantly higher photocatalytic activity when compared to BiOBr-C for the degradation of both pollutants. The degradation rate of MO and Ph by BiOBr-G was found to be nearly 23% and 16% more when compared to BiOBr-C under visible light irradiation, respectively. The substantial increase in the photocatalytic performance of BiOBr-G was ascribed to the multiple synergistic effects between the efficient solar energy harvesting, narrower band gap, high specific surface area, porosity, and effective charge separation. Furthermore, BiOBr-G displayed high stability for five cycles of photocatalytic activity, which endows its practical application as a green photocatalyst in the long run.